I have a code base of 32-bit tasm/tlink (Borland), masm, and 386link (Pharlap/TNT) using mostly calculation but INT 21 for read/write/print. Where are code samples and/or guidance on how to wrapper and convert them to run under cmd/4dos in Windows 7 64-bit OS?

The calculations performed analyze the human heart and have saved many lives - a pretty good reason to keep them. Scripting is vital to the testing of the codes and the tools to accomplish that are in assembly. The specific compilers/linkers mentioned are NOT important. Running those tools in a 64-bit environment is important. Looking for Visual Studio 2008 or later environment to wrapper the tools.

INT21 is a no-go under 64bit OSes - they simply cannot run 16bit code. Yes, I realized the code is 32bit, but since it's dos-extended it has reliance on 16bit startup (and the intricacies of 16<>32bit switching).

If you aren't depending on dos-extended specifics and you only interface with the system for read/write/print, porting to 32bit console application (I don't suppose you're doing graphics stuff?) should be easy, though - ReadFile/WriteFile, or the *Console family of functions if you need to do text-mode "gui" stuff.